origen=new File('dump.txt').text.split('\n') as List
new File('errors.txt').withReader{ reader ->
line=''
while( line=reader.readLine() ){
String id=line.split(' ')[0] //(1)
origen.removeIf{ it.startsWith(id) } //(2)
}
}
new File('cleaned.txt').withWriter('ISO-8859-1',{
it.write origen.join('\n') //(3)
})